Bosch W3CS sparkplugs - should I change?

[Dennis Kalma]

Hi guys, just getting ready to buy new sparkplugs, I have been using Bosch W3CS which are very cold silver electrode plugs. They were the plugs recommeded by Kremer (the guys who built the engine) and so I am tempted to stick with them, even though they run about $6 or so per plug.

The engine is a 3.2 upgrade on a 3.0 case, high compression Mahle P/C's - 9.8:1 compression, CIS, running on Shell pump gas (premium, which is 91 CLC octane here in Calgary).

Recommendations?


Dennis

[Flat Six, Inc.]

Seems a little cold but I would stick with what Kremer said to use.....they are very knowledgeable.

[Steve@Rennsport]

Dennis:

Those are damned cold plugs for a N/A car used for the street. We use those for 930's on the track.

Unless I was running at high RPM's in 5th gear for periods of time, I would likely choose something warmer for better fuel economy & drivability.

[Flat Six, Inc.]

Steve's got a point........Kremer probably had the autobahn or the race track in mind.

I'm using W5DCs in my Euro SC with 9.8:1........but I'm thinking about trying a colder plug like a W4CS to help with detonation.

I tried a colder plug in my BMW motorcycle (R1150GS) and it eliminated my pinging problem.

[Dennis Kalma]

In terms of drivability I have had no problems with the W3CS, but then again, that is the only plug I have used for the life of the engine (now at 25,000 km....so still new!). When I pull them, they are black but show no signs of distress.

Wonder if I should try a set of W4CS to see what happens, but then again I am mortally fearful of detonation.

I assume that the warmer plug would reduce the number of misfires? Is that the source of the better fuel economy and driveability?

Merry Christmas All!

Dennis

[Steve@Rennsport]

Dennis:

Spark plugs are a VERY complex subject,......

The short answer is that each plug has an optimal operating temperature and running above that can trigger detonation. Lower temps create misfires from incomplete combustion and that affects HP as well as fuel consumption.

One learns to perform "plug cuts" to read the plugs and see if they are operating at optimal temps in an engine (and this is now a lost art). Many people have come to rely on AFR instruments to perform that function and thats not the same thing.


Aaron:

LOL,...I'd submit that using a colder plug to mask-suppress detonation is a band-aid and one should first tweak AFR's and ignition timing to that end. Once those parameters are optimized, one chooses plug heat ranges based on the car's usage.

[Flat Six, Inc.]

Steve........my car is a very long story and I totally agree with your point. The car is getting converted to twin-plug MFI anyway......

The BMW.....I didn't have much choice....and it worked.

[A930Rocket]

Steve and Guys,

Not to hijack, but when I rebuilt my engine and had the heads twin plugged, they machine the 2nd plug for a 5/8'' plug. Rather than use two types of plugs, they recomended the same 12 plugs, which is a Bosch FR5DTC. What do you guys think of these for a turbocharged 930 making 400 rwhp (on modified CIS). It a 90% track car running 100 octane and the A/F ratios were good when we dynoed it.

[Steve@Rennsport]

Jim:

I use the smaller plugs (12mm) for the bottom ones on turbocharged or very high-compression motors. This helps preserve mass in the heads and reduces potential cracking. In these examples, I use colder plugs for track use, too.

IMHO, the FR5DTC's are little warm for your motor and I'd use at least a "4" for what you do.

[A930Rocket]

Thanks for getting back so fast Steve.

That would be a 4 as in FR4DTC's?

Jim

Originally posted by Steve@Rennsport
Jim:

I use the smaller plugs (12mm) for the bottom ones on turbocharged or very high-compression motors. This helps preserve mass in the heads and reduces potential cracking. In these examples, I use colder plugs for track use, too.

IMHO, the FR5DTC's are little warm for your motor and I'd use at least a "4" for what you do.

[Steve@Rennsport]

Originally posted by A930Rocket
Thanks for getting back so fast Steve.

That would be a 4 as in FR4DTC's?

Jim

My pleasure,..

Yessir, although I'm pretty sure that Bosch doesn't make anything colder in that design (FRx DTC). I looked inside all my Bosch manuals and 5 is the coldest in that line.

Since its still a 14mm plug, you might use the W4DC or W4CS if you have room.

[A930Rocket]

Thanks again. I couldn't find a FR4DTC either, so I'll look for one one of the others.

JIm